A water body characterized by nutrient rich water supports abundant growth of phytoplanktons and other water plants on its surface. Over time, the water body gets filled with a large number of such plants and the process is called Eutrophication. In such water bodies, dissolved oxygen content is nil or very less.
There is an extremely low level of dissolved oxygen in a eutrophicated water body because:

Options

A. Excessive growth of bacterial decomposers feeding on dead material which consume the dissolved oxygen
B. Plants grow to such a great extent that they do not allow free flow of water hence oxygen in the atmosphere does not get mixed with water.
C. The dissolved oxygen in water reacts with minerals and nutrients to form compounds and hence greatly reduces the quantity of oxygen.
D. Oxygen released is consumed by fishes in the eutrophicated water and hence the quantity of dissolved oxygen is very low.

Answer

A

Explanation

There is an extremely low level of dissolved oxygen in a eutrophicated water body because excessive growth of bacterials decomposers feeding on dead material which consume the dissolved oxygen